This invention relates to heavy-material carrying apparatuses, and more particularly to arm mechanisms capable of moving heavy materials in a two-dimensional plane, for instance, a vertical plane.
It is known that apparatuses such as chain blocks and hoists are used for the movement of heavy materials or loads. However, such apparatuses are disadvantageous in that they cannot positively handle heavy materials in safety and are applicable to only some cargo work, and not to all cargo work, that is, their application is limited to some extent.
Therefore, a variety of heavy-material carrying apparatuses relatively simple in construction and convenient for the movement of heavy materials have been proposed. These apparatuses are, in general, of the small crane type, and are of the so-called dynamic type balance mechanism having an arm mechanism which is composed by links coupled one to another, so that when a load is held by a load holding section, such as a hook, of the apparatus, the section is free from the effect of gravity. Such arm mechanism comprises a parallelogram link mechanism formed by first, second, third and fourth links rotatably coupled to one another, sliding members respectively provided at the coupling point of the first and fourth links and at a free end of an arm extended from the third arm, guide members respectively provided for the sliding members, and a load holding section provided at a free end of an arm extended from the second link. By sliding the sliding members by a driving mechanism, balance of the arm mechanism is maintained while the load holding section is moved in a two-dimensional plane. The range, or area of this two-dimensional plane is limited by the combination of the links and the positions of the guide mechanisms because the arm mechanism employs a parallelogram link mechanism.
The conventional arm mechanism will be described in more detail with reference to FIG. 1. The apparatus comprises: a relatively flat parallelogram link mechanism A-B-C-D having four links 1, 2, 3 and 4 which are rotatably coupled to one another at coupling points A, B, C and D; an arm 2a forming one solid unit with the link 2; a load holding section F provided on the arm 2a on one side of the link mechanism; and guide mechanisms 5 and 6 provided on the other side of the same for sliding member provided on the coupling point D and a sliding member provided on a free end portion of an arm extended from the link 3.
In the apparatus thus organized, the load holding secton F is below the guide mechanism 5, and cannot be moved higher than the level of the guide mechanism 5. Therefore, in order to lift a load, it is necessary to install the apparatus higher than the level of the load by using, for instance, a tall support. Furthermore, since an end part of the link mechanism is above the load holding section at all times as is apparent from FIG. 1, when the apparatus is operated in a room having a ceiling or beams above, the end part of the link mechanism is liable to touch the ceiling or the beams, thus obstructing the operation of the apparatus. This trouble will be frequently caused especially when the load holding section is raised to its uppermost level.